12 bolt width, and wheel/tire fitment

Status
Not open for further replies.

fonz3482

Apprentice
Mar 7, 2011
53
1
0
eden, ny
Hello everyone, I recently posted a thread in the monte section about some rear axle options I had. Well I have decided to go with a 12 bolt so I looked further into the 12 bolt my dads had stashed away for years. Its from a 1972 pontaic gto, its posi, with 4.11 gears. It needs some work because its been sitting in a shed for over 20 years. So I have a few concerns: What is the width of the gto 12 bolt and how much wider is it than my stock 7.5"? What backspacing will I need to keep the tires tucked under the wheel wells? I plan on running 15" wheels and tires for now, so whats the widest rear tires that might fit under the car with the 12 bolt? And what would everyone do to prep a rear end thats been sitting unused for 20 years to be bolted into my monte? Any help or advice would be great, thanks!
 

G_Body_Enthusiast

Royal Smart Person
Supporting Member
Feb 28, 2005
1,056
16
38
Louisville, kentucky
http://www.roadkillcustoms.com/hot-rods ... Widths.asp

if the stock rear is 58 inches and the 12 bolt is 62.5 you can run an extra 2 inches of back space on your wheels and they will come out but a smidgen but if you want them to come out a bit further you can go for 6 or 5.5 back space.

i think a 10 inch wheel is about the widest you're gonna get in the wheel wells before you get rubbing issues and that largely depends more on how big the tire is on the wheel rather than the size of the wheel itself. of course if you come out too much you'll rub the inner lip of the quarter panel and you dont want that. if the body of the car is not sitting on the frame straight you may run into rubbing issues on one side but not the other, so new body bushings would help fix that.

with a 17x8 wheel you can run a 4.5 back space but if you put the 12 bolt in you'll need 6.5 inches. this is just an example. basically add 2 inches to the back space of any wheel you like and that will be the "corrected" back space for the wheel with that rear. 6 inch of back space would probably work as well but i'd watch the width of the tires you put in. it will bring the wheels out an extra 3/4" on each side. my suggestion would be to measure measure and then measure some more before getting new wheels and tires. unless you like that "my tires and wheels stick out from the wheel wells" look i see some people sporting. i think those are people who didnt do their homework before getting the new wheels. dont be one of those people please.
 

robhowardiii

Apprentice
Mar 6, 2012
56
0
0
Just throwing it out there, camaro iroc wheels fit perfect with the wider A body rear. That's what I am running and the backspacing was ideal.
 

JBreu

Royal Smart Person
Jul 15, 2008
2,168
20
38
Livonia, New York
You should get the 12 bolt swap kit from UMIPerformance.com, as the upper ears have a different angle. I have a 12 bolt in my Monte and I had 15x10 with 6.5 backspacing and I just recently traded for 15x8 with 4.5 backspacing....I have Nitto 275x60x15 tires on them now and I get a little rub. Go with the 50 series tire, 26" high vs. the almost 28" that the 60 series are and you should be good. My next set of tires will be the Mickey Thompson ET STreet tires 26x10.5x15 :) As for the prep work , just change the fluid and get new axle seals and you should be all set. My pics have both wheels I mentioned and either way they both look good. Your Dad is a great guy to hand that over to ya :)
 

pontiacgp

blank
Mar 31, 2006
29,270
20,391
113
Kitchener, Ontario
robhowardiii said:
Just throwing it out there, camaro iroc wheels fit perfect with the wider A body rear. That's what I am running and the backspacing was ideal.

what year is the rear end from?.....64-67 is 2.5" wider and 68 - 72 is 4.5" wider than the G body rear.
 
Status
Not open for further replies.

GBodyForum is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to amazon.com. Amazon, the Amazon logo, AmazonSupply, and the AmazonSupply logo are trademarks of Amazon.com, Inc. or its affiliates.

Please support GBodyForum Sponsors

Classic Truck Consoles Dixie Restoration Depot UMI Performance

Contact [email protected] for info on becoming a sponsor